This invention relates generally to inflatable restraint systems and, more particularly, to an apparatus and method for inflating an inflatable device such as an inflatable vehicle occupant restraint for use in such systems.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag cushion," that is inflated or expanded with gas such as when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated, in a matter of no more than a few milliseconds, with gas produced or supplied by a device commonly referred to as an "inflator."
Many types of inflator devices have been disclosed in the art for the inflating of one or more inflatable restraint system airbag cushions. Prior art inflator devices include compressed stored gas inflators, pyrotechnic inflators and hybrid inflators. Unfortunately, each of these types of inflator devices has been subject to certain disadvantages such as greater than desired weight and space requirements, production of undesired or non-preferred combustion products in greater than desired amounts, and production or emission of gases at a greater than desired temperature, for example.
In view of these and other related or similar problems and shortcomings, a new type of inflator, called a "fluid fueled inflator," has been developed. Such inflators are the subject of commonly assigned Smith et al., U.S. Pat. No. 5,470,104, issued Nov. 28, 1995; Rink, U.S. Pat. No. 5,494,312, issued Feb. 27, 1996; and Rink et al., U.S. Pat. No. 5,531,473, issued Jul. 2, 1996, the disclosures of which are fully incorporated herein by reference.
Such inflator devices typically utilize a fuel material in the form of a fluid, e.g., in the form of a gas, liquid, finely divided solid, or one or more combinations thereof, in the formation of an inflation gas for an airbag. In one such inflator device, the fluid fuel material is burned to produce gas which contacts a quantity of stored pressurized gas to produce inflation gas for use in inflating a respective inflatable device.
While such an inflator can successfully overcome, at least in part, some of the problems commonly associated with the above-identified prior types of inflator devices, there is a continuing need and demand for further improvements such as may relate to one or more performance feature or characteristic such as the safety, simplicity, effectiveness, economy and reliability of the inflation apparatus and associated techniques used for inflating an inflatable device such as an airbag cushion.
While some potential problems or disadvantages may be associated with the inclusion of large quantities of water (perhaps up to or more than about 75% by volume) in airbag inflation fluids or if and when such inflation fluids contain water at too high a temperature, it is clear that inflation fluids such as used for safety restraint airbags can contain or include water. As will be appreciated and as further detailed below, numerous additional or possible advantages and benefits may be associated with the potential use of water-reactive compounds for gas generation. For example, in such uses, water may provide a relatively low cost reactant. In addition, water, as compared to typical gases, is of relatively high density and thus a comparatively large amount of water can be stored in a given storage volume. Further, water is a relatively low molecular weight material which may provide or result in comparatively large molar or volumetric quantities of reaction products.
While various water-reactive compounds are available, the more widespread incorporation of water-reactive compounds in airbag gas generating formulations has generally been restricted by factors such as those relating to safe and effective manufacture and use. For example, alkali metals (i.e., lithium, sodium, potassium, cesium, rubidium and francium) are generally among the most chemically reactive of all the metals. In pure forms, such alkali metals are generally so water-reactive that they would normally have to be stored completely separated from the water, such as to avoid undesired or premature reaction. As will be appreciated, the need for such separate storage and containment may undesirably increase manufacturing and production complexity, increase cost and concomitantly reduce performance and operation reliability.
Other metals (such as magnesium, zirconium, titanium and zinc, for example) are also reactive with water. While these metals or various forms thereof are commonly added to or known for inclusion in various pyrotechnic formulations such as used in gas generation for airbag cushions, the reactivity of these metals is generally dependent on factors such as relating to particle size and distribution, purity, content of any absorbed gases and surface characteristics.
Compounds of hydrogen and one or more nonmetals are commonly called or referred to as molecular hydrides. The molecular hydrides of boron are water-reactive and are generally called boranes. There are numerous known borane species. The formula for boron hydrides commonly range from the boron anions, B.sup.n H.sub.n.sup.2- (where n=6-12) to species such as B.sub.n H.sub.n+4 and B.sub.n H.sub.n+6. While the details of the chemical nature of boranes are generally beyond the scope of this description, borane molecules have generally been described as "closed-cage," typically polyhedral, and "open-cage" structures.
Due to the high energy (e.g., high heat of combustion) content characteristically associated with boron hydrides, such materials have been deemed as potential high-energy rocket or jet fuels. Boranes, however, posses many properties or characteristics that may render them unsuitable for common inflatable restraint airbag applications. For example, borane compounds are often susceptible to one or more of the following shortcomings or drawbacks: high toxicity, pyrophoricity (e.g., subject to spontaneous ignition when exposed to air), thermal instability at room temperature and subject to violent reactivity with water.
Thus, there remains a need and a demand for an inflator device such as may permit the low pressure, perhaps atmospheric pressure, storage of reactants or gas generating materials in combination with at least some of the desirable features of the above-referenced fluid fuel inflators. In particular, there exists a need and demand for an inflator device which desirably may facilitate or otherwise more easily permit the advantageous use of such water-reactive compounds which avoid or minimize one or more of the shortcoming or limitations relating to the prior use of water-reactive compounds for such inflation applications.